Thanks very much, Denman, for posting that link. I've wanted a service manual for years.
I recently started a new forum thread titled "Why is the lower seal so much thinner than the upper seal?" after I noticed the new lower seal I was preparing to glue is as thin as the old lower seal. They're 5/16 inch thick, much thinner than the upper seal. In the AppliancePartsPros product image, the lower seal looks like it's supposed to be about 1/2 inch thick, judging from the grid behind it.
Page 68 of the service manual has a photo of new drum seals, which I've attached below. It wasn't shot from the optimal angle to compare the thicknesses of the lower and upper seals. Nevertheless it appears the lower seal is designed to be thinner than the upper seal, assuming the photo shows the correct parts. But this assumption shouldn't be taken for granted, because a single mistake by Frigidaire about the specs for the lower seal could explain both why the lower seal is too thin to make a good seal and why it's thin in the photo. If Frigidaire made a mistake, we're all buying the wrong part, even though it has the right part number.
In the newer forum thread, I describe how I demonstrated a leak all the way around the old thin lower seal... I was able to easily slip a paper clip into the drum through the gap between the lower seal & drum, without applying force. Anyone can do this test by simply raising the top of the dryer (so you can reach down into it). Straighten a paper clip, bend the paper clip about 90 degrees a couple inches from one end, and test whether you can easily slide the end of the paper clip between the lower seal and the lip of the drum. (Don't force it in; you don't want to scratch the lip of the drum. No need for force... it's a good seal where it doesn't slide in easily.)
The service manual contains inconsistencies about the possible causes of overheating:
Page 45 of the service manual is unclear about whether a leak can cause the thermal fuse to blow. It lumps leaks together with other kinds of air flow problems where it lists the possible symptoms: "Airflow problems are usually caused by restrictions, leaks or short unrestricted vents resulting in longer drying times, hotter dryer surfaces and in extreme cases causing the thermal limiter to open on electric dryers." I don't believe short unrestricted vents can cause the thermal limiter (a.k.a thermal fuse) to open, because I think short unrestricted vents would have the opposite effect... wastefully expelling too much heat out the exhaust. If I'm right about that, it means the sentence failed to be sufficiently specific, and thus it doesn't imply whether or not a leak can blow the thermal limiter.
Page 52 has a table of error codes. Code E 8C means the high limit thermostat trips frequently. I presume this would relate to some types of overheating problems. The possible causes listed in the table include leaky drum seals, but not a defective control thermostat: "Check for blocked lint filter, blocked exhaust, air leaks around air duct, broken blower fan blades, worn or loose drum seals, dryer installed in closet with solid doors or door seal not correctly seated."
Page 58 has a flowchart for troubleshooting of overheating. Unfortunately, the word "overheating" is vague since there are four types:
1. Clothes damaged by heat when the control switch is set to "low heat."
2. Dryer failing to cool off or stay at room temperature when the control switch is set to "no heat."
3. Dryer cabinet overheating (and thermal fuse possibly blowing) after the clothes are dry or nearly dry.
4. Dryer cabinet overheating (and thermal fuse possibly blowing) while the clothes are still wet.
To avoid wasting time testing irrelevant parts, each type of overheating should have its own troubleshooting flowchart, or the flowchart should begin with questions about the type of overheating.
The troubleshooting flowchart doesn't mention the possibility of leaks. (Nor the possibility of a partially shorted heating coil putting out more heat than designed.) The only possible causes it lists are air flow restrictions, a defective control thermistor or a defective control board. For my old dryer model, thermistor translates to thermostat (which would need to be diagnosed differently than a thermistor) and "control board" translates to the fabric temperature control (a 4-position switch & resistor network that sets the bias offset temperature of the control thermostat, and can be set to "air fluff" to completely disable the heat).
The control thermistor (or thermostat) and the control board (or fabric temperature control) obviously are possible causes of the first two types of overheating--clothes damaged by heat or the dryer heating when set to "no heat." And I think they might cause the third type--overheating of the cabinet after the clothes are dry. But I'm not convinced they can cause the fourth type--overheating of the cabinet while the clothes are wet--since I think a well-designed dryer should keep the heat fully on while the clothes are wet (so the clothes will dry as fast as possible, to reduce wear & tear on the clothes & dryer, to reduce power consumption, and to save time). Dryers should be designed not to overheat when the heat is fully on, if there are no air flow problems (so that nearly all of the heated air will be sucked into the back of the drum) and the clothes are wet (so that evaporative cooling will keep the drum and exhaust ducts from getting too hot). Evaporative cooling will keep the exhaust temperature low, causing the control thermostat to keep the heat fully on, until the clothes are nearly dry. If this is true, it means the control thermostat and the fabric temperature control are irrelevant to overheating type 4.
MargretS attached the following image(s):
